template_method

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Template Method Design Pattern

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Definition

The Template Method Design Pattern is a behavioral pattern that defines the skeleton of an algorithm in a method, deferring some steps to subclasses. It allows subclasses to redefine certain steps of an algorithm without changing its overall structure. This promotes code reuse and enforces a consistent process while still allowing flexibility for specific behaviors.

Example in Real World/Nature Inspired

1. Cooking Recipes: A recipe lays out the steps to prepare a dish (boil water, add pasta, cook for 10 minutes), but the exact type of ingredients or seasoning may vary depending on the dish.
2. Morning Routines: People generally follow a similar routine in the morning (wake up, brush teeth, have breakfast), but specific steps like choice of food or exercise may differ.
3. Construction Process: Building a house follows a general plan (lay foundation, build structure, install utilities), but the style and materials may vary with each project.
4. Plant Growth: The process of germination, growth, flowering, and reproduction is generally the same across plants, but specific mechanisms differ between species.

Real Usage/System Design Problems

1. Report Generation Systems: A system that generates different types of reports (PDF, Excel, HTML) can use a template method for the overall generation process while letting subclasses implement format-specific logic.
2. Data Parsing/Processing Pipelines: When parsing different file formats (CSV, XML, JSON), a template method can define the steps for validation, extraction, and storage, allowing format-specific details to be implemented in subclasses.
3. Frameworks with Hook Methods: UI frameworks and testing tools often use the Template Method pattern to allow developers to define hooks (e.g., setup(), teardown()) that fit into a predefined lifecycle.

Important Points of Implementation

• Abstract Class Defines Template: An abstract class implements the template method and defines default behavior for shared steps, while marking others as abstract or overridable.
• Hook Methods: Optional steps can be defined as hooks, giving subclasses the option to override them without being forced to.
• Inversion of Control: This pattern is an example of the "Hollywood Principle" — “Don’t call us, we’ll call you.” The base class controls the algorithm and calls subclass methods at the right time.
• Promotes Code Reuse: Common logic stays in the base class, reducing duplication and improving maintainability.

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